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From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@suse.de>, Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org, jroedel@suse.de
Subject: Re: [PATCH] x86: be more helpful with SMEP faults
Date: Tue, 10 Jun 2014 13:24:36 -0700	[thread overview]
Message-ID: <53976984.4030301@zytor.com> (raw)
In-Reply-To: <20140610201823.GA29302@pd.tnic>

On 06/10/2014 01:18 PM, Borislav Petkov wrote:
>>  static void
>>  show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>> @@ -594,6 +596,11 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code,
>>  
>>  		if (pte && pte_present(*pte) && !pte_exec(*pte))
>>  			printk(nx_warning, from_kuid(&init_user_ns, current_uid()));
>> +		if (pte && pte_present(*pte) && pte_exec(*pte) &&
>> +				(pgd_flags(*pgd) & _PAGE_USER) &&
>> +				static_cpu_has(X86_FEATURE_SMEP) &&
> 
> Btw, we could probably save us this line as CR4 reserved bits should be
> Must-Be-Zero and setting any of those should #GP. And I'm talking about
> pre-SMEP Intel, and AMD machines.
> 
> IOW, if CR4.SMEP is set, it definitely means SMEP is present and
> enabled.
> 
> hpa, that true?
> 

Yes.  Also, the Linux kernel will set or clear X86_FEATURE_SMEP to
match, so the two are redundant.

	-hpa



  reply	other threads:[~2014-06-10 20:25 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-10 19:08 [PATCH] x86: be more helpful with SMEP faults Jiri Kosina
2014-06-10 20:18 ` Borislav Petkov
2014-06-10 20:24   ` H. Peter Anvin [this message]
2014-06-10 20:49     ` Jiri Kosina
2014-06-12  0:58       ` [tip:x86/mm] x86/smep: Be more informative when signalling an SMEP fault tip-bot for Jiri Kosina

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